1. Field of the Invention
The present invention generally relates to push-button tuners for radio receivers and more particularly to a push-button tuner in which two preset broadcasting frequencies can be selectively tuned in by each push-button.
2. Description of Prior Art
Widely known is a push-button tuner comprising a plurality of push-buttons each of which is set to tune in to a preset broadcasting frequency so that a desired broadcasting frequency is tuned in by depressing a selected one of the push-buttons into its actuated position. In such a push-button tuner, usually, only one broadcasting station could be selected by one push-button so that in order to tune in to a plurality of broadcasting stations by push-buttons, it has been required to provide a plurality of push-buttons corresponding in number to the number of the broadcasting stations. To increase the number of the push-buttons, however, it was necessary to enlarge the size of the tuner per se and thus there was a limit as to the number of broadcasting stations which could be selected by using a small sized tuner.
Accordingly, there has been proposed a push-button tuner in which a pair of adjacent tuning members are provided with each push-button disposed therebetween and the selected one of the tuning members is interlinked with the push-button so that two different broadcasting stations can be selected by each push-button, whereby it is made possible to select a number of broadcasting stations which is two times as large as the number of push-buttons. Such as push-button tuner is disclosed in Japanese Patent Application entitled "Push-button Type Tuner", filed on Aug. 21, 1984, and assigned to the same assignee as the present application. In the disclosed push-button tuner, an operation member provided with a drive gear and a pair of tuning members each provided with a driven gear adapted to mesh with the drive gear are supported on a support in a manner such that these members are rotatable, movable frontward/rearward, and can come back to their initial positions. Each tuning member is formed with a threaded portion where a tuning piece is provided movably frontward/rearward. A change-over mechanism is provided between the operation member and each pair of tuning members for effecting a change-over operation so as to cause the operation member to alternatively engage with alternate ones of the pair of tuning members for each reciprocation of the operation member. In this push-button tuner, the tuning member engaged with the operation member and located at the rear actuation position is held by a lock member supported by the support, and tuning is performed through abutting between the tuning piece and an actuator plate interlinked with a variable tuning element. A presetting operation is performed by adjusting the position of the tuning piece through enagagement between the drive and driven gears.
In such a threaded shaft type push-button tuner, the amount of rearward movement of each of the operation shafts and the tuning members toward the rear actuation position is restricted through the abutting engagement between the tuning member and the support. Accordingly, the pressing force applied on the operation member after the tuning member has been moved rearward through the depressing operation of the operation member and the rearward movement has been restricted by the butting against the support, is received by the change-over mechanism for causing the tuning member to engage with the operation member. Thus, there is such a risk that an excessive mechanical force may be applied to the change-over mechanism to thereby cause damage in the change-over mechanism to make the tuning function incapable.